1. Field of the Invention
This invention relates generally to acoustic surface wave devices and more particularly to apparatus for improving the frequency characteristics of acoustic surface wave devices. By providing a density of transducer electrode sets which is greater than the density determined by the design center frequency, more accurate exchange of frequencies above the design center frequency can be achieved between electrode sets.
2. Description of the Prior Art
In acoustic surface wave devices, surface waves are propagated between electro-acoustic transducers. The transducer configurations determine the transfer characteristics of the surface wave device. For example, a surface wave device can be arranged to act as a filter. In applications such as filter devices, the frequency response characteristics are typically specified. By associating the amplitude of overlap of transducer electrodes with local maxima and minima of this time domain representation, the desired frequency characteristics have been obtained in the prior art.
Where f.sub.c is the center frequency of the desired frequency response of the acoustic surface wave transducer, the local maxima or the local minima are typically separated by approximately 1/f.sub.c in the time domain. Thus, electrodes are typically spaced in time (i.e. corresponding to surface wave traversal) 1/2f.sub.c apart at positions corresponding to the local maxima and minima. However, as is well known, the highest frequency which can be accurately transmitted or received by such a sampling density is f.sub.c. Thus, there is a deterioration of the frequency characteristics above the design center frequency in electro-acoustic transducers of the prior art.
Furthermore, it is clear that any attempt to provide improved frequency response must involve both the electrode set generating the acoustic surface waves and the electrode set detecting the presence of acoustic surface waves. The accuracy of the acoustic surface wave device frequency response is determined by the least accurate response of the two electrode sets.
It is therefore an object of the present invention to provide an improved electro-acoustic device.
It is a further object of the present invention to provide an improved electro-acoustic transducer.
It is another object of the present invention to provide a surface wave device with improved frequency fidelity above a design center frequency.
It is a still further object of the present invention to provide an electro-acoustic transducer with an increased density of electrodes.
It is yet a further object of the present invention to improve the frequency response of an acoustic surface wave device by increasing the sampling density of input and output transducers.
It is yet another object of the present invention to provide for reduction of spurious signal components resulting from the incorporation of increased electrode densities in an acoustic surface wave device.
These and other features of the present invention will be understood upon reading of the following description in conjunction with the drawings.